.NET is pseudocode that compiles to IL (Intermediate language). After that, it’s JIT (just in time) compiled into platform-specific code. You can push to any platform as long as you have a JIT compiler that can compile to it. It was initially known as Mono on Linux. Microsoft subsequently purchased the project, which was a good thing because it ensured platform parity.

This isn’t a novel concept, by the way. In the early 2000s, Microsoft floated the idea. I should also mention that.NET Core is being phased out as the whole framework in.NET 5 catches up to the functionality of Core.

There’s one more thing. Technically, the most platform-compatible version was.NET Standard. Although Core was close, Standard was small enough to ensure that everything worked on all platforms. However, as time went on, more and more Core functions became cross-platform, effectively flattening the offerings (you could run most of Core on any platform anyway, even earlier on). It’s now being flattened again, and now that Microsoft controls the foundation on other platforms, the goal is to ensure that everything works on all of them. As a result,.NET 5 were released.